Ultra-compact, high-performance motor controller and method of using same

ABSTRACT

Featured is a controller for a motor that is ultra-compact, with a power density of at least about 20 watts per cubic cm (W/cm 3 ). The controller utilizes a common ground for power circuitry, which energizes the windings of the motor, and the signal circuitry, which controls this energization responsive to signals from one or more sensors. Also, the ground is held at a stable potential without galvanic isolation. The circuits, their components and connectors are sized and located to minimize their inductance and heat is dissipated by conduction to the controller&#39;s exterior such as by a thermally conductive and electrically insulating material (e.g., potable epoxy). The controller uses a single current sensor for plural windings and preferably a single heat sensor within the controller. The body of the controller can also function as the sole plug connector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 10/672,888, filed Sep. 26, 2003, which claims priority under 35U.S.C.§119(e) of U.S. Provisional Application No. 60/414,044, filed Sep.26, 2002. This application also claims the benefit of U.S. ProvisionalApplication Ser. No. 60/615,490 filed Sep. 30, 2004 and U.S. ProvisionalApplication Ser. No. 60/699,564 filed Jul. 15, 2005, the teachings ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates in general to controllers for electrical motorsand their use topology. More specifically, it relates to anultra-compact, high performance controller for use on an associatedmotor that has at least one motor winding that carries an electricalcurrent controlled by the controller, and a network of suchmotor-controllers.

BACKGROUND OF THE INVENTION

Every day modern consumers and workers are aided by dozens of electricmotors, which convert electric current and voltage into torques andmotions. These motors adjust the seats, windows, mirrors, and evensteering in cars; bring to life the latest robotic pets; power blenders;drive refrigerator and air-conditioner compressors; wash our clothes anddishes; open our canned goods; drill, saw, and sand wood; and on and on.In factories, electric motors drive CNC milling machines, lathes,robotic arms, conveyer belts, fork-lifts, vacuum systems, hydraulicpumps, and air compressors. Even semi-autonomous robots exploring oursolar system use electric motors. The trend is for increased adoption ofhigh performance motors and especially adoption of networks ofdistributed motors.

The extraordinarily dense scale of integrated circuits and otherexponentially improving technologies that support machine intelligence,such as embedded processors, tiny electronic sensors, and evenhigh-density power storage, set expectations that electric actuators,especially their electronic controllers, will follow a similar rapidimprovement trend. But, improvements in electric motor controllers, suchas power-density (W/cm³), have been painfully slow.

This is especially the case for high-performance motor drives that tendto have sophisticated circuits that require a mix of both noisy powercomponents/circuits and noise-sensitive components and circuit signals.Those trained in the art are taught that bringing a noisy componentwithin close proximity to sensitive component increases ElectromagneticInterference (EMI) for the sensitive component. Consequently, thoseskilled in the art keep the noisy component and the sensitive componentspaced apart from each other to significantly minimize if not avoidthis. However, those trained in the art also know that distancing thenoisy and sensitive components increases the impedance across a commonground. Once the integrity of that ground is lost to impedance, noiseeasily corrupts sensitive analog and digital-logic signals.

Faced with this dilemma, those trained in the art apply galvanicisolation (e.g. isolation transformers, active opto-isolators, and thecircuits that support them) liberally to separate noisy and sensitivecomponents/circuits and bypass the ground-impedance issue altogether.This solution also has the advantage of allowing unrestricted airflowfor ample convection cooling. This solution however, is at the cost ofincreased size, increased power requirement and increased complexity.

In direct opposition to the increase in size is the demand for smalleroverall package size to accommodate higher numbers of motors andcontrollers in cramped spaces. The explosive demand for controllers withmore performance in a smaller package thus, grows unabated. It isdifficult, however, to decrease the size substantially without undulyrestricting air flow (e.g., air flow for cooling) which can createinternal hot spots that ultimately lead to controller failure.

It thus would be desirable to provide a controller for a motor that isultra compact, which can be mounted proximal to the motor and which isrelatively insensitive to EMI affects from power-level circuitry. Itwould be particularly desirable to provide such a controller thatembodies a common unipotential ground for noisy power circuitry thatenergizes the windings of the motor as well as the signal circuitry thatcontrols this energization in response to signals from one or moresensors. Such a controller also would be desirably smaller in comparisonto prior art controllers that handle comparable power. It also would bedesirable to provide such a controller having fewer components ascompared to such prior art controllers. It also would be desirable toprovide apparatuses and the like that embody such controllers as well asmethods related thereto. Such controllers preferably would be simple inconstruction and less costly than prior art controllers.

SUMMARY OF THE INVENTION

The present invention features a controller for a motor having an outputelement and at least one stator winding. Such a controller includes apower circuit that controls current in the at least one phase winding ofthe motor, a sensor that observes current in the power circuit, a signalcircuit that controls the power circuit, and an electrical ground commonto the power and the signal circuits. Such a controller also includeselectrical connectors among the ground and the power and signalcircuits. Further, such power and signal circuits, ground, andconnectors are ultra-compact to produce substantially the same potentialthroughout the ground during the operation of the controller.

Controllers according to the present invention are advantageous in anumber of respects as compared to prior art controllers. Suchcontrollers are compact or smaller as compared to prior art controllers,particularly when compared to prior art controllers that handlecomparable power. Such controllers also will be generally lighter ascompared to comparable prior art controllers, which is particularlybeneficial if the motor and controller are located at the actuator endof a robot link.

Such controllers of the present invention embody fewer components ascompared to prior art controllers, especially components that aregenerally bulky and costly (e.g., isolators, wiring for plural axes, EMIcontrol stacks, and fans. A controller of the present inventionpreferably conducts heat being generated within the controller to theexterior of the controller. Such a controller can provide good heatcontrol or heat management without the cost, bulk and power consumptionassociated with the fans as well as other functionalities of convectiontype of cooling systems. Such heat control characteristics of thecontroller beneficially result in a substantially isothermal temperatureprofile within the controller.

Such controllers can be located proximal to the motor it is controllingyet has the beneficial effect of being relatively insensitive to noisethat may be generated by the power level circuitry. Such controllersalso can provide a high-precision positional determination for the motorthat can be preferably achieved without increasing the bulk of thecontroller.

Such controllers can be used or easily adapted for use in motor networktopologies and further to allow for power sharing and power generation.For example, the controller of the present invention can be used tocause power to be generated by one motor/generator that can be utilizedby another motor(s) of the network which in turn can lead to otherbeneficial effects (e.g., reduced wiring size). Such controllers arepreferably constructed so as to be resistant to environmental effectssuch as if the controller were submerged in liquids or corrosive fluidenvironments.

In embodiments of the present invention such a controller furtherincludes a thermally conductive, electrically insulating casting that atleast in part encases the controller (e.g., functionalities of thecontroller) so as to provide a conductive thermal path to communicateheat generated within the controller to its exterior surface. Inparticular embodiments, the conductive path from any point within thecontroller to the exterior surface of the controller is less than apredetermined value such that the internal heat transfer for heatdissipation is principally conductive and sufficient to produce asubstantially isothermal temperature gradient within the controller.

In more particular embodiments, certain functionalities such as thepower transistors are located near the controller's exterior surfacesuch that there is a thin layer of the casting between the functionalityand the exterior surface. In more specific embodiments, thepredetermined value is about 1-3 cm or less and more particularly about2 cm or less and the thin layer is set so as to have a thickness ofgenerally about 1-2 mm, more particularly generally about 1 mm. Infurther embodiments, the sensor includes a single temperature sensorlocated within the controller and the materials comprising the castinginclude but are not limited to an epoxy.

In further embodiments, a transmitted power density of about at least 20watts per cubic centimeter characterizes such a controller and theexternal connectors of the controller are characterized by a very lowinductance. In yet further embodiments, such connectors of thecontroller include a common mode choke for outside serialcommunications. It should be realized that the connectors providecontinuous electrical connection with no isolators.

In further embodiments, the controller ground is a plane of a conductivematerial with a very low inductance. Also the controller furtherincludes shielding to manage EMI.

The power circuitry of a controller of the present invention includes aPC board, plural power transistors mounted on the PC board at itsperiphery, and a DC to DC transformer disposed with respect to saidplural power transistors, more particularly positioned in proximity toor in contact with the power transistors. In particular embodiments, thepower transistors are FET's having heat-conducting backs facingoutwardly and in a conductive heat-transferring relationship with saidcasing.

In further embodiments, the motor windings are plural windings and saidsensor includes a single current sensor that measures the currentsflowing in each of said windings. Also, the single current sensor caninclude a high-speed operational amplifier connected across a highprecision resistor and the electrical connectors connect one lead of theresistor to the ground.

The sensor can include an encoder, such as an optical encoder, thatdetects the position of the output of the motor and is co-located on andintegral with the controller. Also, the conductors that connect theencoder with the signal circuit (e.g., the digital signal processor orDSP) provide the positional detection information. In more particularembodiments, such encoder conductors have a length of less than about 10mm. In conventional uses, high precision encoders normally limit motorRPM due to bandwidth limitations, however, the controller arrangement ofthe present invention such as the short leads or conductors between theencoder and the signal circuitry enable calculation of useful velocityinformation even at extremely low speed.

In further embodiments, two or more controllers can be operably coupledto each other so as to form a network of controllers and theirassociated motors. In particular embodiments, such controllers furtherinclude electrical connectors that are exterior to the controller, wherethe exterior electrical connectors are operably coupled to each other soas to form the network of controllers and associated motors. In moreparticular embodiments, the second electrical connectors interconnectthe signal circuits of each of the controllers to coordinate theenergization of the motor windings of the motors and to control thedistribution of electrical power among the networked motors andcontrollers. In more specific embodiments, the motors, when acted on byan external force/torque, function as generators of electrical powerthat can be distributed throughout the network.

As can be seen from the foregoing, this invention presents anultra-compact motor controller, that can include an integrated precisionoptical position sensor for use with a motor having a “full size,multi-amp” power rating (above the “milliamp” level, but below that ofheavy industrial motors that draw hundreds of amperes). In an exemplaryillustrative embodiment, the entire coin-shaped, 44-gm weight,controller package measures only 17 cm³. This extreme small size formfactor is smaller than most optical encoders and resolvers of similarprecision, yet the motor-control performance, especially in the controlof torque and minimization of torque ripple, competes with mostfull-size multi-amp controllers including those that are 1000 timeslarger. A low-profile connector system can be integrated into theoverall packaging volume of 17 cm³, with 44 pins available.

In exemplary embodiments, the present invention features a controllerfor a motor that is ultra-compact, with a power density of at leastabout 20 watts per cubic cm (W/cm³). Such a controller embodies a commonground for noisy power circuitry that energizes the windings of themotor as well as the signal circuitry that controls this energization inresponse to signals from one or more sensors. The circuits, theircomponents and connectors are sized and located to minimize theirinductance. Also, the ground is held at a stable potential without theuse of galvanic isolation. Heat is communicated by conduction from heatgenerating functionalities within the controller to its exterior. Thisconduction is preferably provided by a casting of a thermally conductiveand electrically insulating material such as a potable epoxy. Flutes areformed in the outer surface of the casting (e.g., the outer surface ofthe casting corresponding to the side(s) of the controller) not inthermal communication with the heat sink to transfer heat energy to theouter environment (e.g., atmosphere, fluid medium). Such flutes alsoserve as connectors to exterior wires or connector pins. The controlleruses a single current sensor for plural windings and preferably a singleheat sensor within the controller. The controller can be networked toenhance power efficiency and the body of the controller can function asthe sole plug connector.

A particularly useful application of the invention is to control one ora network of small brushless servo-motors that each powers an associatedjoint of a robot hand, arm, or locomotion.

The foregoing shall not be construed as limiting the scope of thepresent invention as other aspects and embodiments of the invention arediscussed below.

DETAILED DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of thepresent invention, reference is made to the following detaileddescription taken in conjunction with the accompanying drawing figureswherein like reference character denote corresponding parts throughoutthe several views and wherein:

FIG. 1 is a side view of a motor controller according to the presentinvention;

FIGS. 2A,B are various views illustrating an exemplary implementation ofthree motor controllers of the present invention in a robotic wrist of arobotic arm;

FIGS. 3-4 are top and bottom axonometric views of an alternateembodiment for the motor controller according to the present invention;

FIG. 5A is a block diagram schematic view illustrating a conventionalhome-run type of motor wiring topology;

FIG. 5B is an illustrative view of a motor embodied in the conventionalhome-run type of motor wiring topology of FIG. 5A;

FIG. 6A is a block diagram schematic view illustrating a conventionaldistributive or network type of motor wiring topology;

FIG. 6B is an illustrative view of a motor embodied in the conventionaldistributive type of motor wiring topology of FIG. 6A;

FIG. 7A is a block diagram schematic view illustrating a distributive ornetwork type of motor wiring topology according to the presentinvention;

FIG. 7B is an illustrative view of a motor embodying a motor controllerof the present invention in the distributive type of motor wiringtopology of FIG. 7A;

FIGS. 8 and 9 are illustrative side views of a motor controller of thepresent invention having soldered low-profile electrical connections;

FIG. 10 is another illustrative side views of a motor controller of thepresent invention having spring-loaded low-profile electricalconnections;

FIGS. 11A-C are various views illustrating an exemplary arrangement forelectrically connecting the motor controller of the present invention toa motor system and including an EMI shield (FIG. 11B);

FIGS. 12A,B are various views illustrating an exemplary DC-DC Toroid EMIshield for a motor controller of the present invention;

FIG. 13 is an axonometric view of a motor controller of the presentinvention without the casting/protective epoxy to illustrate thearrangement of functionalities of the motor controller and thecompactness of the controller;

FIG. 14 is an illustrative schematic block diagram view of a printedcircuit board primarily for signal-level electronics of the motorcontroller of the present invention;

FIG. 15 is an illustrative schematic diagram view of the printed circuitboard primarily for power-level electronics of the motor controller ofthe present invention;

FIG. 16 is a schematic view illustrating the grounding/shields for amotor controller of the present invention;

FIG. 17 is an illustrated section view showing the physical groundingand shielding scheme used inside a motor controller of the presentinvention; and

FIGS. 18A-C are illustrative block diagrams of an alternative embodimentof the present invention in an ASIC format.

DETAILED DESCRIPTION OF THE INVENTION

There are many possible variations of geometry between the stationaryand moving parts of electric motors. And the relative motion can belinear, rotary, cylindrical, spherical, or any combination comprisingone, two, or many degrees of freedom. This invention is not limited bygeometry or type of motions supported.

There are also many motor constructions, such as servomotors, steppermotors, micro steppers, coreless motors, and induction motors. Some arebrushed, some are brushless, some have permanent magnets, and some not.This invention applies to any motor type in which electrical currentmust be supported through at least one motor winding, whether or notposition feedback is required.

For descriptive clarity, the disclosure of this invention uses generallyaccepted terminology related to a common permanent-magnet, brushlessservomotor: an external set of stationery coils (stator) arrangedcylindrically outside a cylindrically-shaped spinning (rotor) shaftcarrying permanent magnets.

The term “motor” is used in the description of the invention, eventhough, in many modern applications, and as used herein, the distinctionbetween motor and generator dissolves, with the power flow betweenelectrical and mechanical frequently reversing.

For descriptive clarity, this disclosure uses the term “motor body” torefer only to the part of the assembly that includes the windings,magnets, shaft, frame, and bearings.

The term motor body is distinguished from the position sensor and thecontroller in this disclosure.

For descriptive clarity, the meaning of the word “machine” in thecontext of motor drives can range among automobiles, robotic arms, largeindustrial machines, and even small toys. While the description hereinrefers or illustrates use of the present invention in connection with alarge industrial servomotor driven machine, the scope of the presentinvention shall not be so limited.

The term “position sensor” shall be understood to mean or describe asensor that measures or estimates position and/or any time-basedderivative of position, such as velocity and/or acceleration.

The motion-control industry applies two meanings to the word“controller.” In the first definition, the “controller” modulates thelow-level winding voltages and power currents based on mechanical orincreasingly sophisticated electronic commutation to control theposition, velocity, acceleration, and/or torque of a single motor. Otherterms for such a low-level motor controller include “current amplifier”and “servo-drive.”

In the second definition, a high-level controller that is incommunication with all motors in the system orchestrates the position,velocity, acceleration, and/or torque of the whole set of motors toachieve coordinated machine motion. The distinction blurs somewhat whena processor located on the current amplifier has both high-bandwidthcommunication and computation capability powerful enough to perform allof the functions of a high-level controller. Although the primary valueof this invention is in its low-level capabilities, it is alsosimultaneously capable of coordinating a set of motors in a network tocreate coordinated machine motion. Furthermore, the high-levelcomputational burden can be shared by several of the low-level currentamplifiers, which scales well, since the job of the high-levelcontroller grows with the number of axes.

Referring now to FIGS. 1-18 c there is shown an ultra-compact motorcontroller 100 that is suitable for robotics applications and the likeaccording to the present invention. According to one aspect of thepresent invention, such as shown in FIG. 1 the ultra-compact motorcontroller 100 is configured and arranged so as to embody conductioncooling techniques. In particular such an ultra-compact motor controller100 includes a high-thermal-conductivity epoxy casting 101 or, as it isalso termed herein, a “matrix,” or “encasement” to provide both heatconduction and electrical insulation. While complete encapsulation isdescribed to protect the components from dust and liquids, it iscontemplated and thus within the scope of the present invention, if aparticular application allows, for less than a complete encapsulation tobe used.

In alternative embodiments, an enclosure in combination with anelectrically insulating material is used, where the enclosure is ametallic or other material with good heat conduction properties. Theelectrical insulator is disposed within the and in contact with theenclosure. The best practical epoxies (those without highly toxicchemical components) have less than 1% of the thermal conduction ofaluminum.

In an illustrative embodiment, the casting 101 of the ultra-compactmotor controller 100 is a high-thermal-conductivity epoxy (35×10⁻⁰⁴Cal/sec-cm-C) that maintains excellent electrical insulation (200×10¹⁴Ohm/cm) while physically protecting the components. Except for the(protected) optical lens 102 facing the motor and electrical contacts106, the module is substantially sealed from liquid spills andpotentially-conductive or heat insulating dust.

While simple power-conversion devices are sometimes encapsulated inepoxy, higher-capacity controllers (˜>100 W) are generally air-cooledbecause, at scales of several centimeters and larger, theheat-insulating properties of even the best epoxies become intolerable.An advantageous feature of the present invention is that at ultra-smallsize, characteristic heat conduction distances shrink to the point whereknown thermally conductive epoxies exhibit acceptable heat conductioncharacteristics. As such, conduction lends itself to rejecting the heatproduced by heat sources within a device such as a controller viaabutting, typically flat surfaces on a metal component to which thecontroller is mounted, typically a motor housing, that acts as aseparate heat sink. As described in more detail below with respect tothe illustrative exemplary embodiment, the invention also includesfeatures such as flutes 104 formed in a side surface, to enhance thedissipation of heat conduction through the epoxy matrix to thesurrounding ambient air. The controller 100 of the present invention iscapable of roughly 3A RMS continuous output, and several times that atpeak operation.

Stated more generally, the conventional wisdom has been to useconvection air cooling for multi-watt motor controllers. To do soeffectively, and to protect heat-sensitive components, the conventionalwisdom has been to separate components and to avoid encapsulating orotherwise interfering with air flows that produce convection cooling atheat sources within the controller or the like. These designconsiderations lead to large controllers. While ultimately theultra-compact size of the controller 100 of the present invention isdetermined functionally—providing the requisite degree of cooling forthe needed performance—controllers according to the invention formulti-watt robotic and like applications, have a volume of less thanabout 20 cm³.

The required capacity (and so size) of any controller is ultimatelylimited by the anticipated temperature of its hottest component(relative to its rated temperature). In a conventional larger-scaleair-cooled controller, there are many hot spots that are thermallyisolated by relatively long distances across air. Since it is oftenimpractical to monitor all of the hot spots, and since many factors suchas ambient temperature affect the degree of air cooling, controllersmust generally be conservatively oversized for a particular application.The ability to monitor the hottest temperature at all times throughoutthe controller 100 of the present invention means that the smallestpossible controller can be used more safely in a particular application.

More specifically, the relatively good heat conductivity of theultra-small controller 100 of this invention produces and ischaracterized by, temperature differences within the controller thatbecome smaller than in conventionally-sized controllers of comparablepower rating. As a result, it is easier to measure the hottesttemperature in the controller with fewer temperature sensors, and evenonly one temperature sensor. In a preferred embodiment this inventionuses only one temperature sensor inside the controller (in addition toan external thermistor embedded in the motor windings).

As illustrated in FIG. 1, the electronics of the controller of thepresent invention are substantially enclosed in a tough, protective,gas/liquid-tight high-thermal-conductivity epoxy casting 101. Themethods used for creating and applying such epoxy castings are wellknown in the art of epoxy-encapsulating electronic modules. The lens 102protects the laser emitting and read optics of a high-resolution (40,960count per revolution) optical incremental encoder with index pulse. Itis surrounded by protective epoxy 108, which rises ˜0.1 mm 110 above thelens surface to resist scratching while handling and duringinstallation.

Concentric cylindrical steps 114 and perpendicular flat surfaces areused for precision mounting the module while making good thermal contactbetween the one face of the outer casting of the controller 100 and themotor back plate and/or other heat sink. Any surfaces not used foralignment can be textured to enhance the dissipation of the heatconducted from the interior of the controller, through the module 100,to an outer surface where convection cooling can occur. A pin hole 112locks in the angular location of the module so that it can be removedand returned without losing calibrated position with respect to theindex pulse. Although not shown, it is a simple matter to embed threadinserts on the faces of the flat epoxy surfaces. This technique ofembedding thread inserts is straightforward in the art of castingelectronics.

Each flute 104 can expose an electrical contact 106 from one (or both)of the boards. The contacts are formed, for example, by locatingconventional plated through-holes around a diameter during the normalboard-fabrication process, and then routing across the diameters of thebias to cut them in half, exposing the plated face, during the normalprocess of releasing the circuit boards from their panels. Counter toconventional practice (for insulated layers), however, it is necessaryto anchor every via on each of the printed-circuit-board layers with aring of copper that intersects the via face. The penetration of theanchors in the preferred embodiment is at least 0.2 mm.

Referring to FIGS. 2A,B, there is illustrated an implementation of threecontroller modules 100 according to the present invention in the roboticwrist, FIG. 2A, of a robotic arm and FIG. 2B illustrates theinstallation features. The alignment pin 116 and engagement 118 of thecylindrical alignment shoulder properly aligns the controller within aplane. Fully seating the controller face 120 with preload from aBelleville spring washer 122, adjusted by cap threads 124, ensuresproper perpendicularity and standoff distance (1.75 mm) between thereflective surface of the Micro-E brand glass encoder scale 126 (whichis adapted 128 to the motor shaft) and the encoder lens surface 130.

FIGS. 3, 4 present how the controller of the present invention can beapplied to an alternate structure, such as a hybrid, bare-die system 131with an integrated laser optical encoder 130 plus the followingsubcomponent die types 134: power MOSFETs and diodes, analog and digitalICs, mixed-signal ICs, and opto-electronic ICs. Integrating dissimilarsemiconductor dies 134 onto a single substrate in this manner yieldseven smaller size, better heat transfer, and further reducesinter-component spacing. Single ASIC controller design would also yielda tighter geometry allowing the design innovations of this applicationto be optimally met.

For the bare-die example, using epoxies selected for proper CTE(coefficient of thermal expansion), the discrete and low density dies134 could be bonded to the ceramic substrate 140. Cracking risks due tothermal cycling can be minimized by matching the CTEs of the die, epoxy,and substrate. After die attachment, the die pads 134 can be wire bonded136 to the substrate 140. Attaching the large, power MOSFETS is asimilar process, except that it's preferable to use a eutectic bondingalloy in lieu of epoxy for better heat transfer. A flip-chip mountingstrategy for high density devices, such as the processor, isrecommended.

The power converter transformer, normally the tallest electricalcomponent, can be wound into the ceramic substrate with flat coppertracks 142. Ferrite material can be located above and below the woundportion of substrate to efficiently conduct magnetic flux. Beyondcooling and compactness, planar magnetics 142 offer ease of manufactureand highly predictable properties. It also is contemplated that carefulshielding techniques are employed to mitigate the risk of the windingvoltage transients capacitively coupling into neighboring circuits.

Power semiconductor die thermal resistance values can be well below 1°C./W. But once packaged, that value can jump to 10's or 100's of ° C./W.Without manufacturer packaging, heat can be pulled directly out of thedies into ambience. An assembly potted using a thermally conductive,highly filled epoxy resin is ideal. Less than a millimeter of epoxybetween the dies and the outside package surface 144 could be achieved.Epoxy shrinkage during curing should not be an issue, as a good epoxyformulation is not expected to shrink significantly on such a smallpackage. J-leads 132 would make it easy to provide a simplesocket-pluggable package.

For machines that use several motors, known motor-wiring topologies aregenerally categorized as either: 1) Home-run (most installed systemstoday) illustrated in FIG. 5A and FIG. 5B; or 2) or network ordistributive systems illustrated in FIG. 6A and FIG. 6B.

Nearly all machine systems 150 today use the home-run topologyillustrated in FIG. 5A, in which each motor 152 receives its electricpower from, and returns position-sensor information to, a controllercabinet 156 located off the moving structure of the machine. Thecontroller cabinet 156 generally contains one current amplifier module158 per motor-driven axis. For example, general-use robotic armstypically have six motor driven axes and so require six currentamplifiers. In general, the cabinet also houses power-supply modules 160that provide both motor-winding and logic voltages to the currentamplifiers.

The motor 152 of FIG. 5A, which is detailed in FIG. 5B, is a typicalprior art motor with at least one winding. It consists of the motor body162 that transmits motions and torques 166 through a rotating shaft orrotor 164. Three power wires 170, 170A carrying Phase A power, 170Bcarrying Phase B power, and 170C carrying Phase C power, togetherprovide the power to three motor windings (three windings is the mostcommon case), combined in either a delta or Y-shaped topology. Thereferred embodiment connects the windings inside the motor body in aY-shaped topology, because the delta winding can allow an unobservableand uncontrollable current around the delta that degrades the precisionof torque control and increases torque ripple. Separate earth groundingfor safety and EMI control (not shown in Figures) is achieved by anyconnected combination of electrically-conducting machine structure andgrounding braids.

Position sensing of the angular orientation of the rotor 164 istypically in the form of three Hall-effect sensors embedded in thewindings of the motor body and an optical incremental encoder 168. Thesedevices transmit position information through signal wires 172 and 174.The motor 152 uses the following signals are used for position feedbackin the general case: 172A is Hall power; 172B is Hall return; 172C isHall 1; 172D is Hall 2; 172E is Hall 3; 174A is Encoder LED power; 174Bis Encoder LED return and ground potential; 174C is A+ pulse train; 174Dis A− pulse train; 174E is B+ pulse train; 174F is B− pulse train; 174Gis Index+; and 174H is Index−.

When the optical incremental encoder 168 of a brushless motor isinitially powered on, it can report position changes, includingdirection. However, until the encoder has rotated past itsonce-per-revolution index pulse, it does not know the absolute rotorposition and cannot support electronic commutation. Until each motor hasrotated far enough to identify its index pulse, the five signal wires172A-172E support Hall-effect transducers provide crude-but-immediatesix-step motor commutation information allowing each motor to be poweredand rotate far enough to identify its index pulse.

Once the index pulses have been located under six-step control, theeight signal wires 174A-174H are used to transmit optical incrementalencoder signals which have much higher precision than the Hall-effectsensors. Although not all optical encoders output differentially drivensignals (174D, 174F, 174H), it is conventional prudent practice, giventhe long and electrically noisy transmission distances between themotors and the controller cabinet along where it is often impractical toseparate substantially the power and signal lines. There are many otherapproaches and variations to measuring motor position, including brushedcommutation without position feedback, estimating position based onback-EMF, absolute optical encoders, resolvers, potentiometers, andHall-only sensors. Each has performance and reliability tradeoffs, butfor high reliability and high performance, the 13 wire arrangement(172A-E and 174A-H) for position feedback is a generally acceptedpractice.

Some motors may have fewer than the sixteen wires (170A-174H), by usinga different position-sensing scheme, or may have more than sixteen wireswhen, for example, motor temperature is monitored or a brake isimplemented at the motor.

Typical robotic arms have six degree of freedom axes, so it is common tohave 50 to 100 wires or more exiting the base of a robotic arm 154,carried through a conduit to its remote controller cabinet 156. Thesewires are also carried into the moving structure of the machine 150where they must withstand high flexing and abrasion. The design of themachine must accommodate, manage, and shield these wires while havingextra power to overcome their resistance to flexing.

Even though the routing of wires through a complex and constantlyflexing multi-joint machine creates serious design and reliabilityissues, the overwhelming majority of industrial machinery relies on thisscheme because it minimizes bulk in the active part of the machine whileconsolidating power supplies, and protecting sensitive electronics fromdirt and liquids.

A network or distributive topology, e.g., the network controllerillustrated in FIG. 6A, though far less common than home-run motorsystems, has potential benefits which have been understood for manyyears. The network topology dramatically reduces the number of wires 180carried through the machine. It relocates the bulk (volume and weight)of controllers 186 out on the machine structure, next to the associatedmotors 178. The increased mass must be carried by the often-movingstructure. And, importantly, if the effective motor dimensions increasefrom the added controller bulk, the machine may need very-expensivemechanical redesign before adoption can be considered. Furthermore, anetwork controller is limited by the communications bandwidth of ashared serial bus.

FIG. 6B details the key components of a networked controller, in whichmotor body 162 and position sensor 168 are connected to a localcontroller 186 by power wires 190, encoder wires 188, and Hall-effectwires 189. This additional controller bulk 186 is a significant fractionof the motor+encoder+controller bulk and may explain why networkcontrollers have not been more widely adopted. Wires 192 exiting thenetworked motor 178 consist of: Bus Power+ 192A, Bus Power Return 192B,Bus Serial Communications+ 192C, and Bus Serial Communications Return192D.

These wires are connected to the machine bus wires 180. Nominally,network controllers operate on four wires 180 (plus a ground path forsafety) consisting of two bus power wires 182 and two bus serialcommunications wires 184. Often, more wires are used because theelectronics that are now located at the motor generally need additional(logic-level) power supply voltages, for example to power opticalisolators. If these additional power levels are generated locally ateach motor controller, the controller bulk increases even further. Theadded-bulk drawback is a major reason why networked motors have remaineduncommon.

If network controllers added zero bulk, they would be far more appealingto machine manufacturers, who could retrofit their existing installedbase of machines. They could also rapidly adopt the technology in newmachines without costly and disruptive major mechanical redesigns.

The controller 100 of the present invention can be used in a newtopology described with reference to FIGS. 7A and 7B. The machine 194 ofFIG. 7A contains a network of motors 196 that share the same bus 180 astypical conventionally networked motors. However, as illustrated in FIG.7B, the encoder and Hall sensors can be integrated into the controller200, attached directly to the motor body 162, so that the entire systemoccupies zero additional bulk over otherwise equivalent conventionalhome-run systems. The reduction of a significant bulk of wires andassociated connectors, and soldered connections near the motor betweenFIG. 6 to FIG. 7 is substantial, and the opportunities for the injectionof electrical noise over several centimeters of wire is reduced to onlyseveral millimeters of printed circuit-board traces. While motor-bodysize 162 tends to scale with power requirements, position sensors andsensor wiring remain relatively constant in size. The tree motor phaseleads 198A-C terminate directly onto the edge of the controller,protected by channels termed herein “flutes” 104: 198A (Phase A); 198B(Phase B); 198C (Phase C). Bus wires 192A-D terminate from the otherdirection in four more edge flutes 104 of the controller 200. Withwireless or signal-over-power bus techniques, the total number of buswires may be reduced to only two, though the preferred embodiment usesfour wires to make integration with other systems more straight forward.

According to another aspect of the, which also departs from conventionalcontrollers, involves folding the encoder (and optionally theHall-sensors) directly into the controller electronics. This eliminatesa great deal of redundant electronics, packaging, and hook-up wiring.The reduction of wires and connectors subtracts substantial bulk andeliminates their role in behaving as EMI (electromagnetic interference)antennae. Much of the support electronics required in an encoder, exceptfor the actual laser optics, are already available on the controllerelectronics. Therefore, a great deal of electronics bulk is eliminated.In the exemplary controller described below in detail, laser-opticcomponents that support 40,960 encoder counts per motor turn occupy lessthan 1 cm³. Also, there is no isolation required, as conductors carryingsignals from the encoder to control circuitry can be, as noted above,very short and have a sufficiently large cross-sectional area that theirinductance L is negligible for motor current switched at thehigh-frequencies normally associated with motor drives.

Wire connections are critical in a controller design of this smallscale. While the multiple-amp currents remain large, the space isexceedingly small. Any conventional connector, such as a miniature-D-subconnector, would double the effective size of the module. The preferredembodiment integrates a connection scheme that adds substantially zerovolume to the overall motor-plus-controller package.

FIGS. 8 and 9 illustrate an arrangement where power 206 and signal 208wires are permanently soldered to the module. In each case, theinsulation 202, 204 is held firm in a flute 210, 212 that is sized to bejust slightly less wide than the insulation diameter. The tight fit withinsulation ensures good strain relief 218, 220 with the module. The endsof the flute are rounded 226 to protect insulation from abrasion as itexits the flute. Tinned conductors 214, 216 are exposed within the fluteregion and match the wire diameter 206, 208 for a secure solder joint222, 224. As seen most clearly in FIG. 9, the depth of the flutes may bedesigned, as they are in the preferred embodiment, to extend theinsulations very slightly (e.g. ˜0.1 mm) above the cylindrical outerdiameter of the electronics module so that a ring, tape, or tangs may beused to further clamp the insulations in place to maximize robust strainrelief. FIGS. 8 and 9 also show an auxiliary cylindrical alignmentfeature 114, 228 that can accommodate alternate mounting strategies.

FIGS. 10 and 11 illustrate one of many possibilities for treating theentire controller module as a single, multi-conductor connector throughthe use of flexible contacts. Even in cases where the module willultimately be permanently soldered in place, such a connector featurefacilitates efficient quality checking of modules before and after beingcast in epoxy to form the casting 101.

Variations can be used for installations of the controller 100 intoparticular machines. The controller module 100 fits into connector 230which consists of a printed-circuit board host ring 232, the outer edge234 of which can be extended outwardly in any shape to support anyquality-checking electronic hardware or connection headers. Platedthrough holes 236 in the printed circuit board host accommodate flexiblepower 238 and signal 240 beryllium-copper pins, anchored by solder 242,244. A bend 246, 248 in the pins combined with chamfered ends 250, 252enable the pins to slide smoothly in the flute and up on top of theelectrical contacts. Thread inserts on the epoxy face 254, combined withthe alignment shoulder 228 or the opposite features on the other (hiddenin this view) side of the controller can help to hold the module firmlyaligned. Alternately the entire module may be clamped against thealignment shoulder on the opposite face. In FIG. 11A, the 35-mmcontroller outer diameter 255 is centered within the connector ring,allowing some clearance in the flute 268 for the associated anchoredpins 270. The cross-section of the connection in FIG. 11B exposes theepoxy matrix 276 from which the flutes are formed. Pins are guided bythe flute sidewalls 272 upon installation. When in final position,spring pressure maintains a reliable electrical contact 274. Thecross-section of the ring 277 in FIG. 11C illustrates the spring motionresulting from removal of the controller.

A toroidal transformer 260 in FIG. 12, the largest single component inthe controller, is nested just inside the semi-circle of MOSFETs. Thetransformer is at the heart of the ability to convert the single motorbus voltage from 18-100 vdc into multiple logic Vcc voltages. Since thetoroid is a major EMI emitter, it is shielded separately in its ownclam-shell-like insulated solid-copper-foil shield 280 that is varnishinsulated and grounded at a single point 284.

FIG. 13 illustrates that inside the surrounding, protective epoxy module100, the controller has top 256 and bottom 258 ten-layer, generallymutually parallel spaced, printed-circuit boards that segregate thevolume of the motor controller substantially into three layered regions,a signal-level, a somewhat quiet top region 288 (normally facing theassociated motor back); a tall, noisy, sandwiched region 290; and aquiet bottom region 292 (facing away from the motor). Large power-supplycapacitors 296 associated with the transformer are stacked in order tooptimize utilization of the available vertical sandwiched space 290. Tohelp contain the EMI to the sandwiched region, one or more of the boardlayers closest to the sandwiched region contain copper ground shields280. In one form, the shields are conventional metallic shielding thatis embedded in the P.C. boards 256, 258, and selectively activated by anelectrical connection. Other known shielding can be used. In particular,circuits and discrete circuit components that are particularly noisy canbe specially shielded.

Though it could be any shape, the preferred shape for the boards 256 and258 is essentially circular and flat to fit within the form factor ofmost conventional optical incremental encoders, and to minimize themaximum distance of the farthest component from centroid of thecontroller 100. This compactness consideration is significant not onlybecause of the EMI, inductance, and heat considerations noted above, butalso because in encapsulating the circuit elements in epoxy, as theepoxy cures, it shrinks. As it shrinks or otherwise degrades, it canpull components on a board and shear them away, or degrade theelectrical connection. The compactness of the present invention resiststhis effect.

Note that alternate embodiments of this invention could take many otherforms, including, but not limited to: a single board containing bothcircuits 256 and 258, or circuits 256 and 258 on two separate boardsconnected by flexible Mylar interconnect.

In the exemplary design of FIG. 13, six power MOSFETs 298 are placedside-by-side, standing upright in a semicircle just inside of the outeredge of the board with their heat sinks 304 facing outwards to optimizeheat transfer to the surrounding epoxy matrix 276 for conduction andelimination from the controller. Of course, while six MOSFETs is idealfor the preferred application described herein, a d.c. brushless motorof a robotic device, those skilled in the art will recognize that adifferent number may be more appropriate in other cases.

Board-to-board electrical connections 294 are implemented in theillustrated embodiment shown in FIG. 13 by eighteen stiff, “vertical”(axially oriented) solid-wire conductors located along the periphery ofthe boards for assembly accessibility. The boards are fixtured duringsoldering so that the wires space the boards, e.g. at 9.5 mm.

The top region 288 is dominated by a CPU (central processing unit) 300.Optionally, there is space for integral Hall-sensor motor-positionsensing 302. A Micro-E brand optical-incremental-encoder read-head 266is integrated directly onto the top board, offset from the board centerin this illustrative embodiment by 6 mm so that the read-head is alignedwith an optical radius from a conventional reflective optical wheelmounted on the end of the rotating motor shaft. The combination yields40,960 A-B counts per revolution of the motor shaft plus one indexpulse. At this level of precision, the controller can be used formetrology applications as well as commutation. The incremental cost foradding position sensing, even at this level of precision, is currentlyonly US$50, which is competitive with stand-alone encoders of much lowerprecision. The optics have built-in correction for misalignment. Testinghas validated that the controller modules work reliably when simplyinstalled without further alignment.

A small proximity sensor (not shown) can be placed on the centerline ofthe module 100 to measure distance between the controller module and theend of the associated motor shaft. In the robotics application describedin the aforementioned U.S. published application No. US-2004-0103740-A1for “Intelligent, Self-Contained Robotic Hand”, when the motor shaftdrives a worm gear, torque on the worm-wheel axially deflects theslight, inherent motor-shaft compliance away or toward the module.Calibrating output torque versus proximity reading allows DSP (digitalsignal processor). 300 to calculate worm-wheel torque, which can then bebuilt into a control algorithm, for example, to protect the fingers of arobot hand by actively limiting maximum torque.

These boards are termed herein as “Tater” and “FET,” respectively.Description of the Tater board in FIG. 14 begins with the implementationof a central processing unit (CPU) 300 in FIG. 13. FIG. 15 then maps outthe functions of the FET board 258 in FIG. 13. FIG. 16 discloses theground and power distribution scheme. FIG. 17 further illustratesgrounding and shielding, and FIG. 12 shows the shielding technique ofthe toroidal transformer, 260 in FIG. 11B.

Tater board design of this exemplary embodiment is centered on ahigh-temperature, BGA (ball-grid array) version of the Texas InstrumentsTMS320F2812, a 32-bit DSP 306 in FIG. 13. Tater runs the DSP 306 at an80 MHz clock rate, within the 150 MHz rating of the DSP. The BGA packagesize of this DSP is also very small, measuring only 10×10×1 mm=0.1 cm³.

In FIG. 14, DSP 306 contains two event managers, EVA 308 and EVB 310,each of which is capable of providing the specialized space-vectorcommutation pulses that are essential to commutate and control a motor.There is no reason why one cannot control two motors with the basicdesign as disclosed here, except for a small size penalty. However, theillustrated embodiment uses only EVA to control one motor to keepcontroller size within the package size of most encoders of similarperformance to the encoder feature of this controller. Some EVB portshave been reassigned as GPIO (general-purpose input/output).

The serial bus communications 312 uses a tiny common-mode choke 314 tofilter electrical noise in place of the more-commonly usedopto-isolation technique. The serial communications follows the CANbusprotocol, which is supported natively in the DSP 306. An RS232 serialtransceiver 316 and programming and debugging interface 318 enableauxiliary communications for use in programming, development anddebugging. CANbus and the RS232 serial communications are routed toavailable electrical contacts in the flutes, even though a customer willnormally need only the two CANbus contacts. The programming, developmentand debugging contacts are only available before the epoxy is cast asthey are not routed to outside flute contacts.

A 256 Kbit serial EEPROM 320 complements the RAM and Flash memory thatare available onboard the DSP. Duty-cycle current modulation fromunregulated 6 vdc is available from two 50 mA auxiliary power sources322 that can actuate an auto-tensioner (as implemented on the preferredembodiment WAM robotic arm) and/or a robotic braking device exploits theavailable EVB 204 pins that support pulse-width modulation. For each ofthese power sources the pulse-width modulation controls the duty cycleof a MOSFET. When applied to other products, these power sources becomeavailable for other purposes.

The single current sensor feedback 324 is a measure of the current on asingle wire or at a single connection point in each of the three phasesin very fast sequence during space-vector commutation. As discussedabove, measuring in this way overcomes a performance problem with normaltwo- and three-sensor current amplifiers in that it is very difficult tomatch perfectly the slightly different gains and biases of the differentsensors. Not matching these sensors well is a common and significantsource of torque ripple. A conventional thermistor that is embedded inthe motor windings is fed back to the Tater at 326. Bus voltage sensingis fed back at 328. Auxiliary analog signal sensing is fed back at 330.Hall-sensor 332 and strain-gage signals 334 are also fed to thecontroller. The analog signals can be low-pass filtered and clamped forovervoltage or noise suppression in the signal conditioning block 325before being fed into the CPU's analog to digital converter 327.

Logic voltage and current are fed back at 336. A “watch-dog” circuit 338monitors the unregulated 6 vdc logic voltage and disables the inverterif voltage droops too low. A DC power conditioning circuit 340implements a filter. Finally, the DSP clock is implemented in circuit342.

The Hall-effect feedback conditioning circuit 344 allows for different“stuffing options” depending on the type of Halls to be implemented. TheMicroE encoder read-head circuit 346 and a selection circuit forchoosing between the onboard encoder or an external encoder is in thechip encoder 348 and the differential voltage circuit 350 shows thestrain-gage signal-conditioning schematic with stuffing options forfilter tuning. Differential voltage generation circuit 352 showsregulation of the dirty (unregulated) logic-voltage, which are initiatedin fixed sequence per CPU manufacturer specifications, accompanied byCPU “watchdog circuitry”. Logic-power sensing circuitry is shown incircuit 354.

The FET-board schematic is shown in FIG. 15. It consists of a DC-DCconverter circuit 356 that uses a transformer with two secondarywindings to produce two lower, unregulated voltages from the main powerbus: a voltage for the MOSFET drivers and a voltage that is delivered tothe Tater board for further refinement to regulated logic voltages.

The motor drive 358 consists of six MOSFETs (although a different numbermight be used depending on the type of motor) to modulate the windingcurrents based on current feedback from the current sensing andconditioning circuit 360. The single temperature-sensing chip for theentire controller is represented by 362. Bus voltage is measured bycircuit 364.

According to yet another aspect of the present invention, and contraryto conventional design practice, is the use of one winding-currentsensor, such as sensor 324 in FIG. 14, preferably applied to all of thewindings in fast sequence. One sensor is smaller, and wastes less power,than the two or more sensors conventionally used to sense and controlwinding currents. Space-vector control, used in the preferred embodimentfor robotics applications, is a high-torque-precision electroniccommutation technique that provides very high precision control ofwinding currents (and therefore motor torque), while boosting powerefficiency over common six-step commutation. But space-vector controlrequires precise current measurements.

A major and unexpected benefit of using only one current sensor is that,while it provides less direct measurement than two sensors, it actuallyimproves the precision of current-control. A central challenge incurrent sensing with multiple sensors is that each sensor has a slightlydifferent bias and gain which drift slightly differently withtemperature. The differences between any pair of sensors leads tocurrent-sensor errors, a major source of added torque ripple. By usingonly one sensor the sensor bias and gain remain identical under allconditions. A single sensor in the controller of the present inventionmakes torque ripple (which occurs at the frequency of the number ofpoles per revolution) not detectable when this controller was used todrive a WAM-brand robotic arm system sold by Barrett Technology Inc. ofCambridge, Mass., hereinafter “the WAM arm.” Slight motor cogging, whichis generated by the magnets passing close to the islands of ironseparating T-slots in the iron core still exists at the frequency of thenumber of T-slots in the iron core per revolution, but this disturbancetorque is easy to cancel, e.g. by using a calibration look-up table. Thetable can be stored permanently on the controller's EEPROM and accessedin real time allowing the table to be applied at any frequency,independent of the serial-bus bandwidth.

FIG. 16 illustrates how grounding is done in the controller, and howderivative voltage levels are created and distributed. The flybackconverter 356, fed by the main bus voltage 368 and high power return386, creates two output voltages: V_LOGIC_RAW 370 to V_LOGIC_RETURN 372(hereinafter referred to as simply V_LOGIC_RAW), which is a floatingoutput, and INVERTER_PWR 374 which is referenced to high power return386.

V_LOGIC_RAW feeds power to the voltage regulators on the Tater board 286on FIG. 13: the 3.3V/1.9V regulator 378 on FIG. 16, and the 5V regulator380. The regulated 3.3V is filtered via the CPU manufacturer'srecommendation for the analog to digital converter 327 (FIG. 14) inpassive filtering 382 in FIG. 16. The filtered voltage is referenced toan analog ground 376 established on Tater 286 (FIG. 13). The filteredvoltage is then fed into a voltage reference 383 (FIG. 16) to create3.0V for an analog signal sensing voltage reference.

Return currents are sent to voltage converter 366 via V_LOGIC_RETURN372. However, the logic ground 384 is tied to high power return 386, ata single point 390, via an electrically quiet, thick, non-currentcarrying path 388. The shielding layers 400 in FIG. 17 in the FET board(258 in FIG. 13) are also tied to high power return 386 in FIG. 16through a single point 391, and thick connection 392. Shield ground isrepresented by 394.

As well as being used on the Tater board 286 (FIG. 13), 5V, 3.3V, andADC3.3V are passed to FET 258. Their return currents are conducted backto Tater through conductor 395 on FIG. 16, and back to logic ground viaa single point connection 396.

Power and communications bussing are done in a network topology. Sincethere is only one power bus, ground looping between multiple powerbusses is not an issue. There is also only one network communicationbus. The CAN bus is protected from spikes of common mode noise andground currents through a common mode choke 314 FIG. 14 inline with theCAN connection in the controller.

FIG. 17 shows the physical shielding and grounding scheme inside thecontroller. The copper routing layers 408 carry sensitive signals. Theselayers are shielded from the noisier routing layers 424, by shieldinglayers 400. Shield layers 400 are tied together at a single point 402,and tied to the high power return layer 282 at that same point 402. Thesingle point connection 402 eliminates current loops within the layers.The positive bus node plane 414 is connected to the bus wire 410. Buspower return 282 is connected at location 412. Bus power return sets thecommon point for the entire controller, and thus is given a thick 1 oz.copper plane so that it conducts high, switched currents with minimalresistive and/or inductive effects. The high power return layer 282 istied to logic ground 422 via a single point connection 406, or asalternately seen at non-current carrying path 388 in FIG. 16.

Power can be seen going from the DC-DC converter 416 on FIG. 17 on theFET board 258 in FIG. 13 to the Tater board 286 via 426 in FIG. 17 andlow inductance conductors 428. The regulator shown at 418 establishes3.3V between planes 420 and 422.

Due to the electrically noisy nature of the components between the FET258 and Tater 286 boards in FIG. 13, there is only one Tater 286 routinglayer 408 in FIG. 17 between the power and ground planes 420 and 422 andthe center cavity. All other Tater 286 in FIG. 13 routing layers 430 inFIG. 17 benefit from the shielding properties of the plane layers 420and 422.

One of the primary EMI noise emitter in the controller is the toroidaltransformer 260. Therefore it is wrapped in a copper foil shield 280,which then gets tied to high power return through the high power returnlayer 282. The shielding blocks harmful EMI from leaving the toroid andinfecting sensitive circuitry, which could cause undesired controlleroperation.

Another noise emitter are the MOSFETs 298 which are carefully placedaround the edge of the controller away from the more sensitive circuitrylocated toward the center. The MOSFETs are populated with their metaldrain-connected tabs facing radially outward, so that during voltageswitching transients the tabs don't spray electrostatic noise intocontroller circuitry.

The controller 100 in FIG. 1 can be organized in functional blocks. Thesingle power bus provides power to 1) the motor amplifier, gate driversand MOSFETs as shown at block 460 in FIG. 18A, and 2) a voltageconverter 462 that in turn powers the feedback block 464, auxiliarydrivers block 468, the microprocessor, logic and memory block 470, and acommunication transceiver block 472 that acts as an I/O interface toexternal data, whether via wires, wireless, or communication over powerline modes. The feedback block receives signals output by sensors suchas conventional Hall sensors, encoders, temperature sensors, and straingauge sensors, all described herein, and otherwise known. The auxiliarydrivers block powers actuators that control, for example, tension incable drives, if used, and joint brakes, if used. The block can, forexample, utilize two MOSFETs that turn on and off a power source that inturn operates an actuator such as a solenoid. The MOSFETs can operate athigh frequencies such as 10 Khz. The motor amplifier, gate driver andMOSFET functional block generates conventional motor drive outputs for aDC brushless motor, or the like.

As a further size reduction alternative, beyond the alternate embodimentillustrated in FIG. 3 and FIG. 4, the functional blocks shown in FIG.18A could be consolidated into functionally similar application specificintegrated circuits (ASICs) and grouped closely together on a substrate,as shown logically in FIG. 18C. The functional chip groupings of theembodiment that makes sense are: FET driver, autotensioner driver,communication line drivers 480; current sensing andamplification/conditioning, strain gage amp, temperature sensing, andposition sensing 486; power MOSFETs 482; and DSP, memory and discretelogic 484.

To achieve the voltage conversion function, presently done by 356 inFIG. 15 it is further contemplated that smaller profile voltageconversion options include: charge pump; different shape transformers(built into the connectors to the puck controller); use of an AC buswith step-down transformer and rectifier (commutation becomes moredifficult but this disadvantage may be offset by other considerations);transformer and other big power conversion circuitry built into motorphase windings; or use of planar magnetic 142 techniques to wind thetransformer into the substrate material.

A second further size reduction implements the motor controllercircuitry of the puck controller 100 in FIG. 1 as one ASIC chiputilizing Very Large Scale Integration (VLSI) on a single silicon chipas shown in FIG. 18B. Both the VLSI chip embodiments, FIG. 18C and FIG.18B produce a much smaller profile than the puck controllers 100utilizing discrete-components on PCB's.

The ready presence and combination of a powerful processor with plentyof volatile and nonvolatile memory at the motor, a wealth of localsensing information, and a knowledge of the state of all motors via theshared communications bus, enables many important functions to becalculated locally, simultaneously improving performance, reducingburden on the serial bus, and reducing the computation and memory ofprocessors outside the network system. The invention as implemented inthe illustrated embodiment(s) exploits this unique capability in severalways. Residual motor-cogging is mapped into a look-up table stored onthe EEPROM. Then the local controller modifies the last torque command,being received at 500 Hz or every 2 msec, as the encoder senses positionchanges. With such a high-resolution encoder, the number of pulses thatwill be received within the 2 msec CANbus delay is significant.

Consequently performance is improved by the ability to calculate andfilter state variables such as velocity and acceleration faster than thecommunications bandwidth. Even at low velocities, logging the precisetime that encoder pulses are received dramatically improves velocityestimation and filtering, which normally suffer from gross discretationerrors. Several control calculations that depend on precise, real-timestate information can then react and change the motor's controlledoutput without waiting for the next 2-msec update. For example, inhaptics, the timely estimation of velocity and acceleration directlyimpact the user's haptic perceptions of damping and inertia. The abilityto poll sensors and recalculate an array of other important valuesquickly compared to the bus frequency can also be applied to gravitycompensation and gravity-vector estimation with the on-boardaccelerometer.

A shared knowledge by each motor controller of the state of all themotors in the system at 500 Hz also allows parallel processing ofhigher-level kinematic matrix calculations. An example is thecalculation of the Jacobian matrix, whose coefficients are functions ofall motor positions. This calculation need not be accomplished as fastas 500 Hz, because it changes only gradually with position changes, butthe computational burden, which would normally require a higher-levelprocessor outside the network system, is no longer required.

Although a preferred embodiment of the invention has been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

Incorporation by Reference

All patents, published patent applications and other referencesdisclosed herein are hereby expressly incorporated by reference in theirentireties by reference.

Equivalents

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. A controller for a motor having an output element and a winding,comprising: a power circuit that controls current in the winding of themotor, a signal circuit that controls the power circuit; an electricalground common to said power and said signal circuits, and electricalconnectors among said ground and said power and said signal circuits,said power and signal circuits, ground, and electrical connectors beingultra-compact to produce substantially the same potential throughoutsaid ground during the operation of the controller, said controllercompactness being characterized by a transmitted power density of aboutat least 20 watts per cubic centimeter.
 2. The controller of claim 1wherein said electrical connectors are characterized by a very lowinductance.
 3. The controller of claim 1 wherein said connectors includea common mode choke.
 4. The controller of claim 1, further comprising asensor that observes current in the power circuit, wherein saidelectrical connectors also connect said sensor to said circuit.
 5. Thecontroller of either of claims 1 and 4 wherein said electricalconnectors provide continuous electrical connection with no isolators.6. The controller of claim 1 wherein said ground is a plane of aconductive material with a very low inductance.
 7. The controller ofclaim 1, further comprising shielding that manages EMI.
 8. Thecontroller of claim 1 further comprising a thermally conductive,electrically insulating casting that at least in part encases saidcontroller to provide a conductive thermal path to communicate heatgenerated within said controller to its exterior surface.
 9. Thecontroller of claim 8 wherein the casting is arranged so that a heatconductive path from any point within the controller to the exteriorsurface of the controller is less than a predetermined value such thatthe internal heat transfer for heat dissipation is principallyconductive and sufficient to produce a substantially isothermaltemperature gradient within the controller.
 10. The controller of claim9, further comprising a temperature sensor, where said sensor includes asingle temperature sensor located within the controller.
 11. Thecontroller of claim 8 wherein material comprising said casting is anepoxy.
 12. The controller of any of claims 8-11 where said castingencapsulates said controller so as to block fluid flow into thecontroller.
 13. The controller of claim 8 wherein said casting is inthermally conducting direct contact with hot spot components of saidpower and signal circuits.
 14. The controller of any of claims 9-11wherein the predetermined value for said casting is one of about 1-3 cm,or less or about 2 cm or less, and a thermal conductivity of the castingis in excess of about 1 W/m-° K.
 15. The controller of claim 8 furthercomprising a heat sink exterior to said casting and in aheat-transmissive relationship with it.
 16. The controller of claim 15wherein said heat sink is a housing of said motor.
 17. The controller ofclaim 15 wherein said casting has flutes on an exterior surface not incontact with said heat sink to facilitate the transfer of heat from saidcasting to the surrounding environment.
 18. The controller of claim 17wherein said flutes are structured to hold a conductor exterior to thecontroller.
 19. The controller of claim 18 wherein said flutes containan electrical contact to one of said electrical connectors of thecontroller adapted to make electrical connection with said conductorreceived in said flute.
 20. The controller either of claim 8 whereinsaid power circuit includes a PC board, plural power transistors mountedon said PC board at its periphery, and a DC to DC transformer that isdisposed centrally with respect to said plural power transistors. 21.The controller of claim 20 wherein said power transistors are FET'shaving heat-conducting backs facing outwardly and in a conductiveheat-transferring relationship with said casing.
 22. The controller ofclaim 1, further comprising a sensor that observes current in the powercircuit, wherein the winding is plural windings and said sensor includesa single current sensor that provides a measurement of the currentsflowing in said plural windings.
 23. The controller of claim 22 whereinsaid single current sensor comprises a high speed operational amplifierconnected across a high precision resistor.
 24. The controller of claim22 wherein said electrical connectors connect one lead of said resistorto said ground.
 25. The controller of either of claims 1 or 8, furthercomprising a position sensor, wherein the active read head of saidposition sensor comprises an encoder that detects the position of theoutput of the motor and is co-located on and integral with thecontroller.
 26. The controller of claim 25 wherein said electricalconnectors connect said encoder with said signal circuit to provide saidpositional information.
 27. The controller of claim 26 wherein saidencoder connectors have a length of less than about 10 mm.
 28. Thecontroller of claims 26 or 27, wherein said encoder is an opticalencoder.
 29. The controller of claim 25 wherein said encoder is enclosedwithin said controller and contributes no additional volume to its bulk.30. The controller of claim 1 further comprising electrical conductorsexterior to the controller and at least one additional one of saidcontrollers, said second electrical conductors forming a network of saidcontrollers and their associated motors.
 31. The controller of claim 29wherein said second electrical conductors interconnect said signalcircuits of each of said controllers to coordinate the energization ofthe motor windings of the motors and to control the distribution ofelectrical power among said networked motors and controllers.
 32. Thecontroller of claim 30 wherein said motors, when acted on by an externalforce, function as generators of electrical power that can bedistributed throughout said network.